1. Field of the Invention
The present invention relates to a display device and, more particularly, to a light emitting diode display device which can facilitate mounting of electrodes and isolation of each light emitting diode element.
2. Description of the Prior Art
It is well known that display devices for visually displaying characters, numeric characters, graphic symbols and the like are divided into two types, namely hybrid and monolithic. In the hybrid type display device, a plurality of light emitting diode chips of predetermined shapes are arranged on a single substrate. In the monolithic type display device, necessary light-emitting diodes are formed in a semiconductor crystal substrate.
In the case of the hybrid type display device, materials can be economically used and a relatively large-scale display can be performed. However, the production process is very complicated and reliability is limited. In addition, luminance tends to vary with the light emitting diode chip and therefore the quality of display leaves much to be desired.
In the case of the monolithic type display device, on the other hand, fine and close display patterns can be easily formed by the use of hot etching or the like and a great number of light emitting regions can be simultaneously formed. Therefore, the display device of this type is suitable for mass production and can almost eliminate variation in the luminance of each light-emitting region. For this reason, the display device of this type is widely used in the display sections of desk computers, wrist watches, measuring instruments and the like.
In producing the above-mentioned monolithic type display device, it is necessary to provide a process for electrically and optically isolating each light-emitting diode formed in a single semiconductor crystal substrate and also a process for forming electrodes and leads for giving drive voltage to each light emitting diode element.
In the case of the conventional monolithic type display device, isolation of each diode element is usually achieved by the following methods:
One is the method in which predetermined regions on the substrate on which P-N junctions are formed are removed by etching and dicing to form a plurality of isolated light emitting diode elements according to the display pattern. The other is the method in which impurities are selectively diffused in the predetermined regions of the substrate to give them a conductivity type opposite to that of the substrate thereby forming a plurality of isolated light emitting diode elements.
In addition, there is proposed a method which bombards the predetermined regions of the substrate with high-energy electrons or protons to make them amorphous so that they are utilized as isolated layers.
However, the above-mentioned conventional methods require complicated processes for the isolation of elements or large-sized expensive apparatuses therefor.
As mentioned above, the isolated elements by the above methods require the formation of electrodes and the connection of leads. For this purpose, vacuum deposition, wire bonding or the like is usually employed. In this case, however, when an increased number of light emitting diode elements must be provided on a single substrate or when the light emitting diode elements are arranged at a close interval in order to perform fine and close display, the processes for forming the electrodes and attaching the leads become very complicated and thereby the yield of production is lowered.